A scalable file may be, e.g., an audio file or video file, such as a JPEG 2000 file wherein the information is stored at different levels. Said mechanism serves the purpose that the same file may be represented in a reduced resolution and/or reduced quality when a high-resolution and high-quality representation is not possible, e.g. due to the available computing performance of the CPU and/or the GPU. In this context, individual information packets of the data stream on the target machine are then discarded, so that the file is reduced to one dimension, e.g. the resolution or the signal-to-noise ratio. From that point of view, the missing decoding resources may be compensated for, on the target machine, by a smaller amount of data to be processed. Advantageous fields of application for such scalable media files are digital movie distributions, archiving and mastering, the file formats advantageously used being JPEG 2000, H.264 SVC or MPEG4 SLC. Image compression methods allowing the storage requirement to be reduced are also frequently used in such applications. In this manner, said image sequences may be compressed to a data rate of up to 250 MBit/s, one having to distinguish between lossy and lossless compression. In digital archiving, the data rates are typically higher than with digital cinema. In order to do justice to this purpose, a profile of its own having an increased data rate of 500 MBit/s is provided in the JPEG 2000 standard.
Real-time reproduction of such files consumes a large amount of resources, it also being possible by now, by using a standard PC, to provide the computing power that may be used for decoding compressed image sequences which may use high data rates by means of current algorithms, new processor families, and graphics cards. However, a further bottleneck in the processing chain of a standard PC has been identified which restricts real-time reproduction in particular with high data rates.
Current consumer hard disks, which typically have a data transmission rate of between 48 and 66 MB/s, are not able to provide the data to a decoder within the appropriate amount of time so as to be able to reproduce an image sequence, e.g. comprising 24 images (frames) per second and a data rate of 84 MB/s, in real time. This applies particularly to external USB hard disks or USB sticks which typically have data transmission rates of between 6 and 19 MB/s. Consequently, the reproduction software and/or the decoder may keep skipping images during reproduction, even if theoretically, the computing power that may be used for the decoding were available.
Current solutions for avoiding this bottleneck are based on utilizing faster hard disks having movable write and read heads. However, said hard disks are costly. A further possibility of ensuring higher data rates between the hard disk and the decoder is to utilize FLASH memories and/or SSD hard disks having data transmission rates of typically 117 to 125 MB/s, it being noted, however, that even in the event of parallel requests for several data streams, for example when reproducing several videos at the same time, a sufficient data rate cannot be guaranteed. Moreover, such FLASH memories are considerably more expensive than normal hard disks. Utilizing faster hard disks is not always possible, and particularly in the future it will have to be expected that image repetition rates as well as the amount of data per frame and, thus, the data throughput that may be used will increase, so that even the above-described generation of hard disks will soon be stretched to its limits. A further possibility of increasing the data throughput consists in combining several hard disks into a so-called RAID (redundant array of independent disks) system. This involves, e.g., using two or four hard disks in parallel to achieve higher writing and reading speeds. In particular with fixed installations, the performance of mass storages is increased by such RAID systems; however, said systems cannot be used, or can be used to a limited extent only, for mobile application (cf. USB hard disks).
Therefore, there is a requirement for an improved approach to overcome performance bottlenecks between the mass storage and the decoder or, generally, a processor.